Navigational Memory in Amnestic Mild Cognitive Impairment Público
Hess, Riikka Erin (2011)
Abstract
Abstract
Navigational Memory in Amnestic Mild Cognitive Impairment
By Riikka Hess
Objective: Patients with amnestic mild cognitive impairment (aMCI) demonstrate impaired explicit memory due to medial temporal lobe dysfunction but relatively preserved implicit memory, which is more broadly mediated within the brain. Many patients have difficulty with navigation in both familiar and unfamiliar environments. Therefore, we assessed the relative contributions of explicit and implicit memory in aMCI and healthy elderly controls (HEC) on a virtual spatial navigation task using the process-dissociation procedure. We expected to find that explicit memory is impaired in aMCI while implicit memory is preserved, as compared to HEC. In navigation, explicit and implicit memory contributions are influenced by practice, such that there is a greater contribution of explicit memory for retrieval of novel mazes and a greater contribution of implicit memory in retrieval of well-learned mazes, with navigational demands held constant.
Participants and Methods: Five HEC and 5 aMCI were trained on 15 virtual T-mazes such that they became well-learned. Following a short delay, participants completed a retrieval task of well-learned mazes. Participants then viewed videos depicting navigation of 15 novel and 15 well-learned mazes. Following a 15 minute-delay, participants navigated the well-learned and novel mazes under both include and exclude conditions. During the include condition, participants were instructed to navigate to the correct exit. In contrast, during the exclude condition, participants were told to navigate to the incorrect exit. This procedure (i.e. the process dissociation approach) provides a method for assessing the relative contributions of explicit and implicit memory.
Results: Given the small sample sizes, the effect sizes for memory contributions are likely better indicators of meaningful differences than the inferential statistics are (none of which reached statistical significance). Considering explicit contributions, there were very large effect sizes for maze type (novel < well-learned) and for the interaction between maze type and diagnosis in explicit memory. Specifically, the contribution of explicit memory in aMCI was comparable to HEC for well-learned mazes but not for novel ones. Implicit contributions were comparable between HEC and aMCI regardless of maze type; however, implicit memory contributed more to navigation of well-learned mazes than novel ones.
Discussion: The results support our prediction that implicit memory is preserved in aMCI and appears to play a major role in the navigation of well-known environments. Conversely, explicit memory deficits in aMCI impede the learning of novel environments. These findings support the development of rehabilitation techniques that encourage greater reliance on implicit spatial memory processes in aMCI. Our conclusions are based on extremely small sample sizes, however, the magnitude of the effects warrants additional study.
Table of Contents
Table of Contents
Introduction...1
Methods...8
Results...14
Discussion...15
Conclusion...19
Appendix A...21
Figure 1...22
Figure 2...23
Figure 3...24
Figure 4...25
Table 1...26
Table 2...27
Table 3...28
Table 4...29
Table 5...30
Figure 5...31
Figure 6...32
Table 6...33
Figure 7...34
Figure 8...35
Table 7...36
References...37
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